Sound recorder and reproducer



Sept. 28, 1937. M. BENDER 2,094,201

I SOUND RECORDER AND REPRODUCER ori inal Filed July 8, 1933 INVENTOR flax. Bender fi'umvnm.

H ATTORNEY Patented Sept. 28, 1937 SOUND RECORDER AND REPRODUCER.

Max Bender, Los Angeles, Calif., assignor, by mesne assignments, to United Acoustigraph Corporation, a corporation of Nevada Original application July 8, 1933, Serial No. 679,465. Divided and this application December 27, 1934, Serial No. 759,345.

uary 15, 1937 Renewed Jan- 8 Claims. (c1. 274-38) This application is a division of my application Serial No. 679,465, filed July 8, 1933.

This invention relates to a recording and reproducing of sound, and has for its object an improved apparatus and method for recording sound in the form of a groove in relatively hard material, such for example, as celluloid or motion picture film. A further object is to provide an improved form of cutting stylus. I

The form of stylus herein disclosed is formed with a curved cutting edge against which the film is moved with the result that the sound groove is formed by the cutting away and removal of a portion of the film in the form of a fine thread.

Other objects and advantages of my invention will appear from the following description taken in connection with the accompanying drawing, wherein:

Figure l is, a vertical central sectional view, partly in elevation of a sound recorder and reproducer embodying one form of my invention;

Figure 2 is a greatlyenlarged side elevation of an improved form of a cutting stylus; and

Figure 3 is. a sectional view taken'on the line 3-3 of Figure 2; and

Figure 4 is a bottom plan view of the structure shown in Figure 2.

Referring. more particularly to Figure 1 of the drawing, reference character It) represents an armature pivoted in bearings,-one of which, II, is shown, which armature is adapted -to be vibrated by an electro-magnet not shown. when the apparatus is used for recording, the electromagnet will carry currents which vary in accordance with variations of the sound to be recorded. The armature I0 is formed with two downward extensions l4 and I5 carrying respectively a reproducing stylus l6 and a recording stylus I'I adapted for engagement with the surface of a film 20. In recording, the film 20 is' moved in the direction of the arrow over an anvil 2| which is formed, at the point of engagement of the film with the cutting stylus, with a relatively sharp curved surface. Figure 1 shows the structure greatly enlarged, the curved upper portion of the anvil for use with the usual motion picture film having a radius less than an inch.

Referring to Figures 2 to 4, the recording stylus i1 is cemented into 'an opening 22 in the lower end of the armature extension l5. The stylus, which is of hard material such as sapphire or diamond, consists of a cylindrical shank 24 which is tapered as indicated at 25. One side of the tapered surface is ground away to form a con cave tapered cutting surface 26 of the stylus.

This surface, in the position of the recorder shown is an upper surface and beneath this surface the taper is ground away to form two lower concave surfaces 21 leaving between them a portion 28 of the original tapered surface 25. The eflect of grinding or under-cutting to form surface 21 is to sharpen the curved edge 30 at opposite sides of the axis of the stylus where the upper surface 26 meets the lower surface of the stylus. As the tapered surface 28 is conical, it is a comparatively simple operation to grind away this surface to a proper depth. The angle a between the upper surface 26 and the portion 28 of the tapered surface 25 should be between 25 and 40 maximum. The angle b as shown in Figure 3, between the surface 21 and the upper surface 26 should be between 20 and 30 maximum. I find that by forming a stylus in this manner with the angles above given, I notonly secure satisfactory cutting but there is sumcient material back of the cutting edge properly to strengthen the stylus and minimize the breakage. In making a sound groove of the lateral cut type, the angle between the surface 28 and the tangent to the film at the cutting point should be approximately 25".

It will, of course, be understood that during the recording operation, the stylus is vibrated by the armature III or other actuating means, in accordance with sound waves to be, recorded and I the recording action is not a scraping or an indenting action on the film but a cutting action. The stylus as described makes a clean cut in the film, removing therefrom a fine thread of the film material.

While in the type of recorder shown, the record groove is of the lateral type, the form of stylus disclosed may also be employed for cutting a groove of the hill and dale or vertical type.

Having now described my invention, what! claim and desire to secure by Letters Patent is:-

1. A recording stylus comprising a shank tapered at one end with the tapered surface cut. away at one side to form with the tapered surface a curved cutting edge at the end of the shank, and the side portions of said edge being sharpened.

2. A recording stylus comprising a shank tapered at one end with the tapered surface at one to sharpen the side portions of said edge.

3. A recording stylus having a shank formed with a conical inclined surface cutting said shank at one end and a second inclined surface cutting said shank at said end and located on the opposite side of said shank to said first named surface and meeting said first named surface in a short 5 cutting edge, and two side surfaces at opposite -15 and meeting said first named surface in a short cutting edge, and two side surfaces at opposite ends of said cutting edge, and inclined to both said first and second named surfaces and forming with one of said first and second named surfaces 20 sharp continuations of said cutting edge, the

angle between said first and second named surfaces being between 25 and 40, and the angle between each of said last named surfaces and said second named surfaces being between 20 and 25 30.

5. A recording stylus comprising a shank tapered to form a conical surface at one end with the conical surface cut away at one side to form with said conical surface a curved cutting edge, and

30 portions of said edge being sharpened by cutting away the conical surface at opposite sides.

6. A recording stylus formed at one end with two oppositely inclined surfaces meeting in a cutting edge, and the material being also cut away to form curved extensions of said edge at opposite ends of said edge.

7. The method of .cutting a sound groove in a hard flexible member by means of a stylus comprising a shank tapered at one end with the tapered surface cut away at one side to form a second tapered cutting surface joining the first named tapered surface in a curved edge and having said edge undercut to sharpen the side portions of said edge, which method consists of maintaining said stylus with said tapered surface at the cutting edge at an angle of approximately 25 to the tangent to the flexible material at the cutting point, moving said material against said edge and causing said stylus to vibrate in accordance with sound waves to be recorded.

8. Means for cutting a sound groove in a hard flexible member, a stylus comprising a shank tapered at one end with the tapered surface cut away at one side to form with the tapered surface a curved cutting edge and having saidedgeundercut to sharpen the side portions of the edge, means for guiding a flexible member against said edge, means for holding the stylus with the edge penetrating the surface of said flexible member and with said tapered surface at the cuttingedge at approximately 25 to the tangent to the surface of the flexible material at the cutting point and means for vibrating the stylus in accordance with the sound to be recorded.

MAX BEN'DER. 

